Fiberboard manufactured with cellulose nanofibrils as a binder and method of making same

ABSTRACT

Fiberboard sheet materials containing cellulosic fibers ae disclosed in which cellulose nanofibrils are used as a binder for adhering the cellulosic fibers together. The cellulose nanofibrils are present in an amount of 0.5% to 7.5% by weight on a dry weight basis of the fiberboard sheet. The fiberboard sheet materials have strength properties that meet or exceed the requirements in ASTM C208, and are useful for structural sheathing and roofing board applications. A process for manufacturing the fiberboard sheet is also disclosed.

FIELD OF THE INVENTION

The present technology relates generally to fiberboard products made from cellulosic fibers. In particular, the present technology relates to fiberboard and fiberboard composites that utilize cellulose nanofibrils (CNF) as a binder for adhering the cellulosic fibers together to form the fiberboard product.

BACKGROUND

Cellulosic fiberboard is used in various construction industry applications, such as insulation board, structural sheathing and roofing cover board. Conventional fiberboard products typically utilize starch or synthetic resins or polymers as a binder for adhering the cellulosic fibers together. Common synthetic resins include phenolic resins, such as phenol resorcinol formaldehyde and phenol formaldehyde, urea-formaldehyde, melamine-formaldehyde, and MDI-isocyanate. One concern associated with these resins is the dangerous emission of formaldehyde, a carcinogen, from formaldehyde-based resins, and the release of toxic gas when MDI-isocyanate binders are burned. Significant research has been devoted to developing alternative binder systems to reduce or eliminate formaldehyde-based and MDI-isocyanate resins from fiberboard products, yet improvement is still needed for a cost-effective binder system for the manufacture of structural fiberboard having strength properties that can meet industry standards.

Starch binders do not have the same emissions issues as synthetic resins, but they also have certain drawbacks. Starch fines can settle out of the fiber slurry during fiberboard manufacturing, and may not be available for bonding the cellulosic fibers together. Starch is also water absorbent, necessitating additional treatments to the fiberboard, or the addition of other additives, to reduce water absorption in the fiberboard. Structural fiberboard panel products utilizing vegetable starch as a binder also may not have the strength properties required by the construction industry.

Fiberboard sheet products must meet certain industry standards if the fiberboard sheet is to be used for structural sheathing or roofing applications. For example, ASTM C208 defines the physical property requirements for cellulosic fiberboard insulating board. In particular, roof insulation board (Type II) and wall sheathing (Type IV) must meet minimum requirements for strength and racking load, among other properties. Roof insulation board should also meet industry standards for wind uplift resistance and hail damage resistance.

It would be desirable to provide a cellulosic fiberboard having strength properties that meet or exceed the requirements in ASTM C208, such as for Type IV Grade 2 wall sheathing, as well as other industry standards, such as wind uplift and hail damage resistance for fiberboard roofing board. It would also be desirable to manufacture a cellulosic fiberboard without the use of common MDI-isocyanate, formaldehyde-urea and phenolic-formaldehyde synthetic resins. Eliminating or reducing the use of these synthetic resins would not only reduce harmful emissions, but could also allow the manufacture of a cellulosic fiberboard product from renewable sources, which is recyclable and therefore more “green”.

SUMMARY OF THE INVENTION

It has now been discovered that cellulose nanofibrils (CNF) can be used as a binder in the wet manufacture of cellulosic fiberboard and fiberboard composites. In some embodiments, the CNF can replace the synthetic resins or starch that are commonly used as binders in cellulosic fiberboard products. Surprisingly, a significant improvement in the strength of fiberboard can be achieved by using cellulose nanofibrils in an amount of 5% by weight or less in the fiberboard, based on the dry weight of the fiberboard components.

One aspect of the present technology is a fiberboard sheet comprising (a) cellulosic fibers in an amount of 81.0-99.0% by weight, on a dry weight basis of the fiberboard sheet; (b) and a binder comprising cellulose nanofibrils, wherein the cellulose nanofibrils have a fiber diameter in the range of 0.01 to 0.3 micrometers, and are present in the fiberboard sheet in an amount of about 0.5% to about 7.5% by weight, on a dry weight basis of the fiberboard sheet, preferably about 0.5% to about 5% by weight on a dry weight basis. In some embodiments, the fiberboard sheet meets or exceeds the strength requirements defined in ASTM C208 for Type IV Grade 2 structural sheathing.

Another aspect of the present technology is a dried fiberboard sheet formed from a wet mat, wherein the wet mat comprises (a) from 81.0-99.0% by dry weight of cellulosic fibers; (b) a binder comprising cellulose nanofibrils having a diameter of about 0.01 to about 0.3 micrometers, wherein the cellulose nanofibrils are present in the wet mat in an amount of about 0.5% to about 7.5% by weight, preferably about 0.5% to about 5% by weight, based on dry weight of the cellulosic fibers and cellulose nanofibrils; and (c) water, wherein the dried fiberboard sheet has a density between 10 lb/ft³ and 31 lb/ft³.

A further aspect of the present technology is a process for manufacturing a fiberboard sheet, and the fiberboard sheet made by the process, wherein the process comprises (a) preparing a fiber slurry comprising cellulosic fibers and water; (b) adding cellulose nanofibrils having a fiber diameter in the range of about 0.01 to about 0.3 micrometers to the fiber slurry in an amount of about 0.5% to about 7.5% by weight, preferably about 0.5% to about 5% based on dry weight of the fiberboard sheet; (c) dewatering the fiber slurry to form a wet mat comprising the cellulosic fibers and cellulose nanofibrils; and (d) drying the wet mat to form the fiberboard sheet.

Another aspect of the present technology is a fiberboard material for use in manufacturing a fiberboard sheet, wherein the fiberboard material comprises (a) cellulosic fibers in an amount of about 81.0% to about 99.0% by weight, based on total dry weight of the fiberboard material; (b) a binder comprising cellulose nanofibrils, wherein the cellulose nanofibrils have a fiber diameter in the range of 0.01 to 0.3 micrometers and are present in an amount of about 0.5% to about 7.5% by weight, preferably about 0.5% to about 5% by weight, based on total dry weight of the fiberboard material; and (c) water.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the modulus of rupture of cellulosic fiberboards as a function of CNF content.

FIG. 2 is a graph showing the effect of CNF having different size, fibril, and fines characteristics on the modulus of rupture of cellulosic fiberboards as a function of CNF content.

FIG. 3 is a graph showing the effect of the order of wax addition on the water absorption of cellulosic fiberboards.

FIG. 4 is a graph showing the transverse strength of cellulosic fiberboards containing 2.5% by dry weight CNF.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

While the presently described technology will be described in connection with one or more preferred embodiments, it will be understood by those skilled in the art that the technology is not limited to only those particular embodiments. To the contrary, the presently described technology includes all alternatives, modifications, and equivalents that can be included within the spirit and scope of the appended claims.

As used herein, fiberboard sheet refers to a fibrous-felted, homogeneous panel made from ligno-cellulosic fibers, having a density of less than 31 lb/ft³ but more than 10 lb/ft³, and characterized by an integral bond which is produced by interfelting of the fibers, but which has not been consolidated under heat and pressure as a separate stage in manufacture.

The term “cellulose nanofibrils” refers to cellulose nano and micro filamentous particles having a branching structure, with at least one dimension in the range of 0.01 to 30 micrometers. Cellulose nanofibrils may also be referred to as “nanocellulose” (NC) or “microfibril cellulose” (MFC).

The terms “dry weight”, “on a dry weight basis”, and “based on dry weight” refer to an amount of a component present without regard to the amount of water that may be present.

The term “about” means+/−10% of the referenced value. In certain embodiments, about means+/−5% of the referenced value, or +/−4% of the referenced value, or +/−3% of the referenced value, or +/−3% of the referenced value, or +/−2% of the referenced value, or +/−1% of the referenced value.

The present invention relates to fiberboard and fiberboard composite sheet materials comprising cellulosic fibers bound together using cellulose nanofibrils as a binder. In particular, the fiberboard sheet materials are manufactured using a wet process, and can be cellulosic fiberboard, fiberboard material, roofing board, roofing board material or other suitable construction material meeting, for example, and preferably ASTM standard C208.

Cellulose Nanofibrils

The cellulose nanofibrils used as a binder in the present technology have diameters in the range of 0.01 to about 0.3 micrometers, preferably about 0.03 to about 0.2 micrometers, as determined by electron microscope analysis. The fibril lengths may vary, but generally are in the range of about 0.5 to about 30 micrometers or more. The cellulose nanofibrils also have a fibrillated structure in which the nanofibrils have significant branching. The dimensions and structure of the cellulose nanofibrils provide a high aspect ratio and large specific surface area that provide a large number of OH-group bonding sites available for hydrogen bonding with the cellulosic fibers in the fiberboard. The greater the amount of fibrillation in the cellulose nanofibrils, the more OH-group bonding sites that are created, which lead to more hydrogen bonding of the cellulosic fibers and greater fiberboard strength. In addition, the branching structure of the cellulose nanofibrils provides interfibrillar entanglements that can physically interact with the cellulosic fibers and enhance the cellulosic fiber bonding and fiberboard strength.

Preferably, the fibril content of the cellulose nanofibrils is in the range of about 30% to about 60%, alternatively about 44% to about 55%. Fibril content can be determined by using a Britt jar filtration technique, which is a gravimetric method of measurement. In the method, a diluted cellulose nanofibril sample is passed through a 76 micron filter. The particles passing through the filter are called fibrils. Fibril content is expressed as a percentage of the fibrils passing through the filter relative to the total amount of cellulose nanofibrils in the sample.

The cellulose nanofibrils are prepared from celluloses derived from wood or non-wood lignocellulose materials, or a combination thereof. Typically, the cellulose nanofibrils are prepared from wood pulp. Some non-wood cellulose sources contemplated herein include hemp, wheat, bamboo, corn stalks, and bagasse, or combinations thereof. Cellulose nanofibrils produced from these non-wood sources may further enhance the properties of the cellulosic fiberboard sheets. The cellulose nanofibrils can be processed from an aqueous suspension of the cellulose source in water using a variety of different processes and devices known in the art. Such processes include high-shear refining, pulp refining, friction grinding using, for example, a supermasscolloider or ceramic beads, and homogenizing using, for example, a high-pressure homogenizer. The cellulose source can also be subjected to an enzymatic or chemical process as a pre-treatment prior to a mechanical refining process. Cellulose nanofibrils are also available commercially from different sources. Most commercially available cellulose nanofibrils are produced from Thermal Mechanical Pulped (TMP) Cellulose. The aqueous suspension containing the cellulose nanofibrils may have a solids content of about 3% to about 15%, and has a paste-like consistency. In some embodiments, the cellulose nanofibril suspension may be further diluted with water to create a homogenous liquid having a low viscosity that provides better distribution in the fiberboard slurry.

Cellulosic Fibers

The cellulosic fibers used for producing the fiberboard sheet of the present technology are prepared from a cellulosic source, which is most commonly wood pulp, although other sources of wood or non-wood cellulosic material could be used. The cellulosic source could also be a combination or wood and non-wood cellulosic materials. The wood pulp or other cellulosic material is broken down into fibers that are capable of being suspended in an aqueous slurry and deposited on a screen in the fiberboard manufacturing process. Fiber sizes for the cellulosic fibers can vary, and include but are not limited to fibers having diameters in the range of about 25.0 to about 30.0 micrometers, and lengths in the range of about 827 to about 1,200 micrometers. The amount of cellulosic fibers in the fiberboard sheet may be about 81.0% to about 99.0%, alternatively about 83% to about 96% by dry weight, based on the dry weight of the components in the fiberboard.

Other Fiberboard Components

The fiberboard sheet may contain one or more additional components, including waxes, starches, alum, and other fillers and agents. For example a wax, such as paraffin, may be added in a concentration of about 0.5% to about 5.0 by dry weight; starch, such as vegetable starch, may be added in a concentration of about 0.5% to about 9% by dry weight; aluminum sulfate may be added in a concentration of about 0.1% weight to about 1.5% by dry weight, and sodium aluminate may be added in a concentration of about 0.1% to about 1% by dry weight, all concentrations based on the total dry weight of the fiberboard components.

In some embodiments, a drainage aid may be included in the slurry to assist in the dewatering process to make the fiberboard sheet. Such drainage aids are typically ionic, but may also be nonionic. Ionic drainage aids may be anionic or cationic. In one embodiment, the drainage aid may be a high molecular weight cationic polymer emulsion. The cationic polymer in the emulsion ionically bonds to the anionic sites on components in the slurry, resulting in agglomeration of the components into bundles called floc. The structure (size/dimensions) and net charge of the floc affect how easily water is removed during fiberboard sheet manufacture. The drainage action is both capillary and charged based. One example of a drainage aid suitable for use in the present technology is AXFLOC AF4820, a high molecular weight cationic polymer available from Axchem USA Inc., Marietta, Ga. The amount of drainage aid employed may be in the range of about 0.5 lbs to about 2 lbs per dry ton of fiberboard components.

Fiberboard Sheet Manufacture

To make the fiberboard sheet of the present technology, the wood pulp is processed in water to form a slurry comprising the cellulosic fibers and water. The solids content of the cellulosic fiber slurry is about 0.8% to about 3.5%. The cellulose nanofibrils are combined with the cellulosic fibers in the slurry such that the cellulose nanofibrils comprise from about 0.5% to about 7.5%, alternatively about 0.5% to about 5%, preferably about 1% to about 3% by weight based on the combined dry weight of the components in the fiberboard slurry. Surprisingly, it has been found that adding less than 5% dry weight of cellulose nanofibrils to the cellulosic fibers can significantly increase the transverse strength of the fiberboard sheet. For example, adding less than 3% dry weight of cellulose nanofibrils to the cellulosic fibers can increase the transverse strength of the fiberboard by 5 times compared to a similar fiberboard sheet made without the cellulose nanofibrils. That such a low amount of cellulose nanofibrils can have such a significant effect on increasing the strength of the fiberboard is surprising because the literature suggests that fiberboard strength increases with increasing amounts of cellulose nanofibrils.

It has also been found that adding amounts of cellulose nanofibrils greater than 5% dry weight can adversely affect water drainage from the cellulose fiber slurry during dewatering to form the cellulosic fiber wet mat, particularly if the cellulose nanofibrils are highly fibrillated. Therefore, in some embodiments, a maximum of 5% dry weight of cellulose nanofibrils is used to make the fiberboard sheet. Less fibrillated cellulose nanofibrils can be used in a greater amount, such as up to about 7.5% by dry weight or more, and still have adequate drainage when making the fiberboard sheet.

The cellulose nanofibrils are typically in the form of a thick paste or gel that is thixotropic. Preferably, the cellulose nanofibrils are diluted in water and mixed to form a homogenous liquid prior to combining the cellulose nanofibrils with the cellulosic fibers. Dilution in water allows the cellulose nanofibrils to be more easily combined with the cellulosic fibers. The amount of water used to dilute the cellulosic nanofibril paste is not critical, and can be any amount that facilitates handling and dispersion of the cellulose nanofibrils, for example a 10:1 dilution of water to cellulose nanofibrils. In some embodiments, the cellulose nanofibril paste may be diluted in water to a concentration of less than 1% solids, or a dilution of 100:1 or less.

In one embodiment, the cellulose nanofibrils are the only binder in the fiberboard and replace 100% of the starch, phenolic resin, or other binder. Without being bound by theory, it is believed that the fibrillated structure, high aspect ratio, and large surface area of the cellulose nanofibrils provide fibril entanglements and a high number of OH-group bonding sites available for hydrogen bonding of the cellulosic fibers, resulting in increased fiberboard strength without the need for other binders. In other embodiments, the cellulose nanofibrils could be used in combination with another binder. For example, the cellulose nanofibrils could be combined with up to about 9%, alternatively up to about 7%, alternatively up to about 5% by dry weight of starch as a binder, with a minimum of at least 0.1%, alternatively at least 0.5% by dry weight of starch. Alternatively, the cellulose nanofibrils could be combined with up to about 10% by dry weight of a polymeric resin binder. In an alternative embodiment, up to about 30% by dry weight of asphalt could be used as a binder in combination with the cellulose nanofibrils.

The cellulose nanofibrils can be combined with the cellulosic fiber slurry by injecting the homogenous liquid containing the cellulose nanofibrils into the slurry prior to dewatering to form the wet mat. If additional components are included in the fiberboard formulation, they can be added and mixed with the cellulose nanofibrils in the homogenous liquid, or added directly to the cellulosic fiber slurry. Surprisingly, in some embodiments, the order of addition of fiberboard components can effect some properties of the resulting fiberboard sheet. For example, in some embodiments, when wax is included as a component of the cellulosic fiber slurry, adding and mixing the wax with the cellulose nanofibrils first can result in less water absorption in the fiberboard sheet than if wax is added directly to the fiberboard slurry.

Preferably, the injection pressure for injecting the homogenous liquid is higher than the pressure applied to the cellulosic fiber slurry at the point of injection. In an alternative embodiment, the diluted cellulose nanofibrils can be applied to the surface of the wet mat during vacuum forming. The cellulose nanofibrils can then flow between the cellulosic fibers in the wet mat, and become entwined and bond the cellulosic fibers together. In a further embodiment, the cellulose nanofibrils could be added to a pigmented clay coating that is applied to the fiberboard after the wet press stage during fiberboard manufacture.

The cellulosic fiber slurry is transported to a screen where water drains through the screen in a dewatering process. Removal of the water results in a wet mat in which the cellulose nanofibrils and cellulose fibers are mechanically interlocked and strongly bound. The mechanical interlocking and hydrogen bonding also tends to retain any other slurry components within the formed wet mat, resulting in fewer particulates and therefore lower turbidity in the water drained during the dewatering process. Increased retention of the slurry components in the formed wet mat increases binding, resulting in a thinner and denser fiberboard in which density can be increased by about 2.0 lbs/cu.ft. compared to that of a fiberboard manufactured without cellulose nanofibrils.

The wet mat is dried to remove additional water, resulting in a fiberboard sheet comprising about 81.0% to about 99% by dry weight of cellulosic fibers, about 0.5% to about 5% by dry weight of cellulose nanofibrils, and having a moisture content of about 1.0% to about 3.0%. The fiberboard sheet has a density between 10 lb/ft³ and 31 lb/ft³.

The fiberboard sheet of the present technology provides several improvements and advantages over prior art fiberboard products. Due to the use of the cellulose nanofibrils as a binder, the fiberboard sheet can be manufactured from renewable resources and is recyclable. The fiberboard sheet also has enhanced strength properties. Without being bound by theory, it is believed that the cellulose nanofibrils provide increased hydrogen bonding sites that enable increased hydrogen bond formation between the fiberboard components, thereby increasing the strength of the fiberboard sheet. The fiberboard sheet of the present technology has a transverse strength greater than a similar fiberboard sheet made with a binder not containing cellulose nanofibrils. The fiberboard sheet of the present technology also has a MOR higher than a similar fiberboard sheet made with a binder not containing cellulose nanofibrils. In some embodiments, the fiberboard sheet of the present technology has strength properties that meet or exceed the racking strength (determined in accordance with ASTM E-72), transverse strength, and MOR requirements for structural sheathing defined in ASTM C208 for Type IV Grade 2, making the fiberboard sheet useful as a structural sheathing product. ASTM C208 specifies a minimum transverse strength of 20 lbf for a ½ inch fiberboard sheet for Type IV, Grade 2 structural sheathing. It is also expected that, due to the enhanced strength properties, the fiberboard sheet, in some embodiments, can have a wind uplift resistance of at least 330 lb/ft² determined in accordance with ANSI/FM4474, FM4450, FM4470, and be resistant to severe or very severe hail damage as assessed in accordance with FM Approvals standards, making the fiberboard sheet useful as roofing board or panel in roofing systems.

In addition to use in cellulosic fiberboard sheets, cellulose nanofibrils could also be used in the manufacture of structural building components, furniture components, and molded automotive panels.

The presently described technology and its advantages will be better understood by reference to the following examples. These examples are provided to describe specific embodiments of the present technology. By providing these specific examples, it is not intended to limit the scope and spirit of the present technology. It will be understood by those skilled in the art that the full scope of the presently described technology encompasses the subject matter defined by the claims appended to this specification, and any alterations, modifications, or equivalents of those claims.

EXAMPLES Example 1

Control and test fiberboard sheets 12×12 inches square were prepared from cellulosic fibers using the general formulation shown in Table 1. The test fiberboard sheets were prepared by substituting a dry weight amount of cellulose nanofibrils for an equal dry weight amount of the cellulosic fibers in the general formulation. Two types of cellulose nanofibrils, Manufacturer 1 Type A CNF (“Mfg 1 Type A”) and Type B CNF (“Mfg 1 Type B”), differing in dimensions of the cellulose nanofibrils, were used in the test fiberboard sheets. Mfg 1 Type A has a nominal fiber width of 30-300 nm and length of 3-30 microns. Mfg 1 Type B has a nominal fiber width of 10-100 nm and a length of 1-10 microns. The amount of cellulose nanofibrils in the test fiberboard sheets varied. Four test fiberboard sheets of each type of cellulose nanofibrils were prepared with test amounts of cellulose nanofibrils of 1.18%, 1.58%, 2.93%, and 5.84% by dry weight, respectively.

TABLE 1 Ingredient Dry fiber (at moisture) Binder starch (4-8%) Wax (0.75-1.5%) Aluminum sulfate (0.2-1%) Sodium aluminate

The formulation components are mixed together, and the mixture is transferred to a mold where it is dewatered. After dewatering, the fiberboard sheet is pressed, oven dried, and cut to appropriate sizes for testing.

The test and control fiberboard sheets are evaluated for transverse strength (lbf) per ASTM C209 using sample strips 3″×11″. Modulus of Rupture (MOR) is calculated from the transverse strength measurements and sample thickness:

-   -   MOR=5×Transverse Strength/(caliper)².

FIG. 1 is a graph showing the MOR of the fiberboard sheets as a function of the cellulose nanofibril content in the fiberboard sheet. As shown in FIG. 1 , fiberboard sheets made with less than 3% dry weight cellulose nanofibrils had MOR values five times greater than the fiberboard sheets made without the cellulose nanofibrils.

Example 2

Test Fiberboard sheets 12×12 inches square were prepared using the general formulation in Table 1, except that no starch was used in the fiberboard formulation. The test fiberboard sheets were prepared by substituting a dry weight amount of cellulose nanofibrils for an equal dry weight amount of the cellulosic fibers in the general formulation. Eight different types of cellulose nanofibrils were used in the test fiberboard sheets. The different cellulose nanofibrils tested were Mfg 1 Type A, Mfg 1 Type B, Manufacturer 2 CNF (“Mfg 2”), Manufacturer 3 Type A CNF (“Mfg 3 Type A”), Type B CNF (“Mfg 3 Type B”), and Type C CNF (Mfg 3 Type C”), and Manufacturer 4 Type A CNF (Mfg 4 Type A″) and Type B CNF (“Mfg 4 Type B”). Mfg 2 CNF is a cellulose nanofibril gel having a solids content of about 3% and nominal fiber width of about 50 nm. Mfg 3, Type A is a cellulose nanofibril suspension having a fibril width of about 20-25 nm and a Britt jar fibril content of about 45-60%, Mfg 3, Type B is a cellulose nanofibril suspension having a fibril width of about 25-35 nm and a Britt jar fibril content of about 25-40%, and Mfg 3, Type C is a cellulose nanofibril suspension having a fibril width of about 18-22 nm and a Britt jar fibril content of about 65-75%. Mfg 4, Types A and B are aqueous dispersions of highly refined or microfibrillated cellulose. The test fiberboard sheets were prepared with each type of CNF at cellulose nanofibril amounts of 1%, 1.5%, and 2% by dry weight. Test fiberboard sheets with 0% CNF served as a control. The fiberboard sheets were evaluated for transverse strength (lbf) per ASTM C209 using test sample strips 3″×11.″ Modulus of Rupture (MOR) for each sheet is calculated using the Example 1 equation. The results are shown in FIG. 2 .

FIG. 2 shows that the MOR can vary with different CNF from different sources. However, the results confirm that MOR increases when CNF is included in the fiberboard sheets, and is generally higher at 2% by dry weight CNF than at 1% or 1.5% by dry weight.

Example 3

In this example, test fiberboard sheets 12×12 inches square were prepared in order to assess whether adding the wax component to the cellulose nanofibrils before adding the cellulose nanofibrils to the cellulose fiber slurry has an effect on water absorption of the fiberboard sheet. The test fiberboard sheets were prepared using the general formulation in Table 1, except that no starch was used in the formulation and 2% dry weight of different cellulose nanofibrils was substituted for an equal dry weight amount of cellulosic fibers. The different cellulose nanofibrils were Mfg 1 Type A, Mfg 1 Type B, Mfg 2, Mfg 3 Type A, and Mfg 3 Type B. The test fiberboard sheets were prepared according to the Example 1 general procedure, except that, for each type of cellulose nanofibril, one test fiberboard sheet was prepared by combining the wax component with the cellulose nanofibrils prior to mixing the fiberboard components together, and a second fiberboard sheet was prepared by mixing the fiberboard components together without premixing the wax and cellulose nanofibrils. The dried test fiberboard sheets were evaluated for water absorption by conducting a 2-hour water absorption test according to ASTM test method C1763. The results are shown in FIG. 3 .

The results show that adding wax to the cellulose nanofibrils prior to mixing the fiberboard components together can result in lower water absorption.

Example 4

A fiberboard sheet manufacturing trial was conducted on a manufacturing line to produce full-sized 4 ft×8 ft fiberboard sheets. A fiberboard slurry was prepared using the general formulation in Table 1. The slurry components are mixed together and cationic drainage aid in an amount of 1-1.2 lbs. per dry ton of fiberboard is added. Cellulose nanofibrils having a fibril content of 50-55% are added at a rate equal to 2.5% by dry weight of the components to replace an equivalent amount of the cellulosic fibers. The mixture is deposited on a Fourdrinier wire which permits free drainage of water from the slurry material. The slurry is dewatered and formed into a wet fiber mat. After dewatering, the fiberboard sheet is pressed, oven dried, and cut into finished 4×8 panels. Test sheet of appropriate sizes for testing were cut from the selected 4×8 sheets. The test fiberboard sheets are evaluated for transverse strength (lbf) per ASTM C209 using sample strips 3″×15″. Modulus of Rupture (MOR) is calculated from the transverse strength measurements and sample thickness:

MOR=6× Transverse Strength/(caliper)². The transverse strength results are shown graphically in FIG. 4 .

The graph in FIG. 4 shows the transverse strength of the fiberboard sheet manufactured before the addition of CNF to the fiberboard slurry (at points R13 and R14 on the graph), the transverse strength of the fiberboard sheet manufactured with CNF added, starting at point F1 through C55 on the graph, and the transverse strength of the fiberboard sheet post-trial, without CNF added (at points R15 and R16). The fiberboard sheet manufactured with 2.5% by dry weight CNF added had transverse strengths that exceeded 20 lbf, as shown in FIG. 4 .

The present technology is now described in such full, clear and concise terms as to enable a person skilled in the art to which it pertains, to practice the same. It is to be understood that the foregoing describes preferred embodiments of the present technology and that modifications may be made therein without departing from the spirit or scope of the present technology as set forth in the appended claims. Further, the examples are provided to not be exhaustive but illustrative of several embodiments that fall within the scope of the claims. 

What is claimed is:
 1. A fiberboard sheet comprising: (a) cellulosic fibers in an amount of 81.0-99.0% by weight on a dry weight basis of the fiberboard sheet; (b) a binder comprising cellulose nanofibrils, wherein the cellulose nanofibrils have a fiber diameter in the range of 0.01 to 0.3 micrometers, and are present in the fiberboard sheet in an amount of about 0.5% to about 7.5% by weight, on a dry weight basis of the fiberboard sheet.
 2. The fiberboard sheet of claim 1, wherein the fiberboard further comprises one or more additional components selected from the group consisting of starches, waxes, alum, fillers, drainage aids, and combinations thereof.
 3. The fiberboard sheet of claim 2, wherein the additional component is vegetable starch in an amount of 0.5-9.0% by dry weight.
 4. The fiberboard sheet of claim 2, wherein the additional component is paraffin wax in an amount of 0.5-5.0% by dry weight.
 5. The fiberboard sheet of claim 2, wherein the additional component is aluminum sulfate in an amount of 0.1-1.5% by dry weight.
 6. The fiberboard sheet of claim 2, wherein the additional component is sodium aluminate in an amount of 0.1-1.0% by dry weight.
 7. The fiberboard sheet of claim 1, wherein the fiberboard sheet is a structural sheathing product or a roofing insulation panel.
 8. The fiberboard sheet of claim 1, wherein the fiberboard sheet has a transverse strength and/or a modulus of rupture (MOR) that meets or exceeds ASTM C208 Type IV Grade
 2. 9. The fiberboard sheet of claim 1, wherein the fiberboard sheet has a racking strength that meets or exceeds ASTM C208 Type IV Grade
 2. 10. The fiberboard sheet of claim 1, wherein the fiberboard sheet has a wind uplift resistance of at least 330 lb/ft² determined in accordance with ANSI/FM4474, FM4450, FM4470.
 11. The fiberboard sheet of claim 1, wherein the fiberboard sheet has a resistance to very severe hail damage, as determined in accordance with FM Approval standards.
 12. A fiberboard material comprising: (a) cellulosic fibers in an amount of 81.0-99.0% by dry weight, (b) a binder comprising cellulose nanofibrils, wherein the cellulose nanofibrils have a fiber diameter in the range of 0.01 to 0.3 micrometers and are present in an amount of about 0.5% to about 7.5% by weight based on dry weight of the cellulosic fibers and cellulose nanofibrils; and (c) water.
 13. A process for manufacturing fiberboard comprising the steps of: (a) preparing a fiber slurry comprising cellulosic fibers and water; (b) adding cellulose nanofibrils having a fiber diameter in the range of about 0.01 to about 0.3 micrometers to the fiber slurry in an amount of about 0.5% to about 7.5% by weight based on dry weight of the cellulosic fibers and cellulose nanofibrils; (c) dewatering the fiber slurry to form a wet mat comprising the cellulosic fibers and cellulose nanofibrils; and (d) drying the wet mat to thereby form the fiberboard.
 14. The process of claim 13, wherein prior to step (b), the cellulose nanofibrils are diluted in water to form a homogenous liquid.
 15. The process of claim 14, wherein the homogenous liquid containing the cellulose nanofibrils is added to the fiber slurry by injecting the liquid into the fiber slurry.
 16. The process of claim 15, wherein the homogenous liquid is injected at a pressure greater than the pressure of the fiber slurry at the point of addition.
 17. The process of claim 13 wherein the process further comprises adding additives to the fiber slurry.
 18. The process of claim 17, wherein the additive comprises starch.
 19. The process of claim 17, wherein the additive comprises a wax.
 20. The process of claim 19, wherein the wax is mixed with the cellulose nanofibrils prior to adding the cellulose nanofibrils to the fiber slurry. 